An ever present concern in the manufacture of paperboard containers is to provide a rigid container which is capable of holding a substantial amount of fluid without collapsing when grasped by the consumer. It is also a major concern that such rigid containers be manufactured in an economical manner to produce a container which will be pleasing to the consumer.
Paper container rigidity is defined by the load which when applied to the side walls of the container deflects the side wall of the container inwardly one quarter of an inch. Further, this test is carried out at a point on the side wall of the container which is two-thirds the height of the overall container. This rigidity test determines the ability of the container to be picked up by the consumer without collapsing inwardly and spilling the contents when the container is grasped by the side wall. The rigidity of a particular container is affected by the tensile and bending stiffness in both the vertical and circumferential directions of the container. One expedient for increasing the rigidity of a paperboard container is to form a brim about the top of the container.
As is disclosed in U.S. Pat. No. 2,473,836 issued to Vixen et al., conventional brim curling mechanism utilizes complimentary curve dies in which the lower die is first moved upwardly around an upper end of the paperboard container to an upper periphery thereof where it firmly holds the cup against the die. The upper die is then moved downwardly to engage the upper periphery of the paperboard container between the dies with both of the dies then moving downwardly together to curl the upper periphery of the container thereby forming a brim. This brim adds significantly to the rigidity of the overall container structure.
Similarly, U.S. Pat. No. 3,065,677 issued to Loeser discloses a brim curling mechanism for paperboard containers. A lower die having a curve forming upper surface is maintained stationary while an upper die having a curve forming lower surface descends downwardly toward the stationary lower die, deflecting the upper edge portion of the cup secured by the lower die and again forming a brim about an upper periphery of the container. This brim as stated previously, adds significantly to the overall rigidity of the container.
As is illustrated in FIG. 1A, each of the above-mentioned containers are formed with the machine direction of the paperboard material aligned in an axial direction of the container and the cross machine direction of the paperboard material aligned in the circumferential direction of the container as shown by the arrows MD.sub.1 and CD.sub.1, respectively. Paperboard material, when formed using conventional paper manufacturing processes, has what is known in the art as a "machine direction and a cross machine direction." The machine direction of the paper is generally that axis of the paper along which the paper is moved as it was being formed. The cross machine direction is perpendicular to the machine direction of the paper and has approximately twice the maximum stretch as that of the machine direction, while the tensile and bending stiffness of the board in the machine direction is greater than that in the cross machine direction. Therefore, in order to easily form brims about the upper periphery of the container, the paperboard blank used in forming the cup is generally positioned as illustrated in FIG. 1A.
In an effort to increase the overall rigidity of the paperboard container and to increase the paperboard container's acceptance by the consumer by eliminating cracks in the brim curl, U.S. Pat. No. 5,029,749 issued to Aloisi and assigned to the assignee of the subject invention proposes reorienting the paperboard material when forming the blanks in accordance with conventional practices. That is, the machine direction of the paperboard material is oriented so as to extend in the circumferential direction of the paperboard container with the cross machine direction of the paperboard container being aligned with the axial direction of the container as illustrated in FIG. 1B. While this orientation of the paperboard material does in fact result in an increased rigidity of the container, the size of the brim curl formed about an upper periphery of the container is limited by the orientation and properties of the paperboard materials. That is, because board stretch in the machine direction is less than that in the cross machine direction the size of brim curls about the upper periphery of the container will be smaller than brim curl of the container illustrated in FIG. 1A.
The use of moisture in aiding in the formation of brim curls has been known as illustrated in European Patent Application No. 0,129,064 wherein a brim forming press for forming brim curls includes a spray and nozzle for producing an annular spray pattern of atomized water and directing such spray on the inside top margin of the annular wall of the cup during engagement of the deflector with an upper periphery of the cup. However, the atomized water is used to lubricate the top margin of the annular cup when forming the brim curls in a convention manner. In doing so, the frictional engagement between the cup and the forming press is lessened.
Similarly, U.S. Pat. No. 2,541,905 issued to Amberg discloses the moistening of the upper portion of a cup in order to form satisfactory brims on the cup. Again, the moistening of the upper portion of the cup is done so as to aid in the formation of a brim curl about the upper periphery of the cup in a conventional manner. This being done at the brim curling station.
In addition to the foregoing, U.S. Pat. No. 1,743,215 issued to Hill discloses a process for the production of paper containers and particularly cup-shaped paperboard containers having rolled rims where the edge rolling step of the process can be executed more advantageously if the edge to be rolled is moistened before being subjected to a rolling process. Herein, as with the above-noted references, the formation of brim curls about an upper periphery of a paperboard container utilizing conventional forming devices can be aided with the use of moisture. Particularly, in U.S. Pat. No. 1,743,215, a stack of disks to be formed into paper cups is formed with the edges of the disks being moistened for edge forming purposes while maintaining the central portion of the disk dry. These disks are then subsequently formed into paper cups using conventional forming devices. That is, the disclosure of Hill has recognized that by subjecting the blanks to moisture, brim curls of a conventional size and shape can be more readily carried out. However, the use of moisture in the Hill disclosure does not increase the overall rigidity of the resultant container.
Clearly, there is a need for a container and more specifically a paperboard container which exhibits an increased degree of rigidity than that previously achieved by producing a paperboard container having an enlarged brim curl about an upper periphery thereof adds to the rigidity of the paperboard container and provides a paperboard container which is more acceptable to the consumer without increasing the basis weight of the paperboard material.